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In the diagram given below, there are three lenses formed. Considering negligible thickness of each of them as compared to [R 1 ] and [R 2 ], i.e., the radii of curvature for upper and lower surfaces of the glass lens, the power of the combination is

1. ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ + | R | 1 | R | 1 6 1 – 2 1
2. ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ | R | 1 – | R | 1 6 1 – 2 1
3. ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ + | R | 1 | R | 1 6 1 2 1
4. ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ | R | 1 – | R | 1 6 1 2 1

Correct answer: ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ | R | 1 – | R | 1 6 1 – 2 1

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